Food waste is a major problem in Canada. Nearly 60% is lost or wasted each year, and short-lived fruits and vegetables are a big part of that. So researchers at the University of Guelph are testing a new kind of edible coating to see if it can extend the shelf life of that most fickle of fruits: avocados.
Angie Homez-Jara and her colleagues tested chitosan, an edible coating derived from the chitin found in the exoskeletons of shellfish and other arthropods, against a chemical commonly used to preserve fruit called 1-methyl-cyclopropene (1-MCP).
They treated mature Hass avocados with 1-MCP or a solution containing either 1% or 1.5% chitosan, and stored them under conditions mimicking commercial transportation and the grocery store – first chilled to 5 degrees C for 21 days, then brought to room temperature until they were rotten. Avocados treated with 1% chitosan lasted 33 days – the same amount of time as untreated fruit. Those treated with 1.5% chitosan or with 1-MCP lasted 42 days, but the chitosan-treated fruit had some unappetizing defects, such as uneven firmness and discoloured spots on the peel. Homez-Jara says the defects were likely related to the permeability of chitosan to oxygen. “It’s didn’t let enough oxygen through for even ripening,” she says.
Homez-Jara has some ideas about how the chitosan could be improved however, by using a concentration somewhere between 1 and 1.5%, or by blending it with other polymers that have different characteristics. “Starch-based polymers have higher oxygen permeability, so perhaps we could balance the two,” she says.
If the kinks can be worked out, chitosan coatings would have several advantages over 1-MCP. Some are related to health and safety of workers. 1-MCP is deposited onto fruit as a gas, and the people applying it need to wear protective gear to avoid being exposed to the vapour. Chitosan, in comparison, is non-toxic and edible and has antimicrobial properties. It is also easily produced, either by extraction from shellfish or by algae fermentation, and as it comes from a natural source it is more environmentally sustainable, says Homez-Jara.
Jayasankar Subramanian, an agricultural researcher at the University of Guelph who was not involved in the research, says chitosan has been getting a lot of attention from the industry recently, and has shown good results in many different fruits. “The efficacy is certainly there and it is a good alternative,” he says.
But Subramanian also wonders whether the shellfish origin could cause problems. Vegetarians and vegans may not want their fruit and vegetables coated in it, and there is also a possibility it could cause allergic reactions. “The one thing that I am yet to see about chitosan is any reports of allergy when someone consumes the fruit coasted with chitosan,” he says. “Mainly chitosan is extracted from shrimp shells, shellfish or other similar marine creatures and so there is a good possibility of allergy.”